exa docs and python package update (#31307)

Added support for new Exa API features. Updated Exa docs and python
package (langchain-exa).

Description

Added support for new Exa API features in the langchain-exa package:
- Added max_characters option for text content
- Added support for summary and custom summary prompts
- Added livecrawl option with "always", "fallback", "never" settings
- Added "auto" option for search type
- Updated documentation and tests

Dependencies
- No new dependencies required. Using existing features from exa-py.

twitter: @theishangoswami

---------

Co-authored-by: Chester Curme <chester.curme@gmail.com>

libs/partners/exa/tests/integration_tests/test_retriever.py

@@ -26,3 +26,19 @@ def test_exa_retriever_highlights() -> None:
     assert isinstance(highlight_scores, list)
     assert isinstance(highlights[0], str)
     assert isinstance(highlight_scores[0], float)
+
+
+def test_exa_retriever_advanced_features() -> None:
+    retriever = ExaSearchRetriever(
+        k=3, text_contents_options={"max_characters": 1000}, summary=True, type="auto"
+    )
+    res = retriever.invoke("best time to visit japan")
+    print(res)  # noqa: T201
+    assert len(res) == 3  # requested k=3
+    assert isinstance(res, list)
+    assert isinstance(res[0], Document)
+    # Verify summary is in metadata
+    assert "summary" in res[0].metadata
+    assert isinstance(res[0].metadata["summary"], str)
+    # Verify text was limited
+    assert len(res[0].page_content) <= 1000

libs/partners/exa/tests/integration_tests/test_search_tool.py

@@ -8,3 +8,23 @@ def test_search_tool() -> None:
     res = tool.invoke({"query": "best time to visit japan", "num_results": 5})
     print(res)  # noqa: T201
     assert not isinstance(res, str)  # str means error for this tool\
+
+
+def test_search_tool_advanced_features() -> None:
+    tool = ExaSearchResults()
+    res = tool.invoke(
+        {
+            "query": "best time to visit japan",
+            "num_results": 3,
+            "text_contents_options": {"max_characters": 1000},
+            "summary": True,
+            "type": "auto",
+        }
+    )
+    print(res)  # noqa: T201
+    assert not isinstance(res, str)  # str means error for this tool
+    assert len(res.results) == 3
+    # Verify summary exists
+    assert hasattr(res.results[0], "summary")
+    # Verify text was limited
+    assert len(res.results[0].text) <= 1000